Thermoplastic materials are increasingly used in a form of molded parts or extruded films or sheets in either monolayer (single composition) or in multilayer composites for applications such as sporting goods, hand held devices, cosmetic articles, and automotive exterior and interior parts. For those applications, the surface appearance of the articles is often of primary importance. Thus, the articles require high scratch and abrasion resistance for maintaining desirable surface aesthetic appearance. Excellent scratch resistance, however, is one of the properties that may be difficult to attain for a thermoplastic material compared to lacquer systems, which are often crosslinked. Coating over articles such as with a polyurethane coating in a post-molding process has often been necessary to attain high scratch resistance. A thermoplastic material with high scratch resistance may eliminate the need for such expensive coating processes. For many applications, equally important are other properties such as toughness, mechanical properties, and processability. Wide latitude of processability for making articles in varied manufacturing processes is especially desirable, which requires that the thermoplastic material exhibits appropriate melt rheology.
There is also an overall need in molded parts, particularly in automotive applications such as bumpers, fender extensions, hub caps, and other fascia components and molded exterior parts, for products that have high gloss, good weatherability, high impact strength and high temperature properties (e.g., tensile strength and dimensional stability such as sag and creep resistance). It is also desirable to be able to mold in solid and metallic colors and, optionally, to be able to paint the parts. “Solid” colors present a homogenous finish, even at very close inspection. All ingredients, which can be substantial in number, are milled and blended such that, when applied, they appear to have been produced from a single, homogenous ingredient. The solid color does not sparkle or brighten when directly illuminated by a light source, nor does it appear to change significantly when viewed from different angles. “Metallic” colors (including pearlescents) contain discrete flake pigments, which can range from pearl flakes to aluminum flakes or mica flakes. These flakes are large enough to be discretely identifiable within the field of color being observed. The metallic color has a noticeable “sparkle” when the surface is directly illuminated with a light source, plus they appear to change in color as the panel is rotated from a perpendicular angle to an oblique one. This property is called “polychromaticity”. This change in color as the viewing angle is rotated is also referred to as “travel” or “flop”.
Ionomers are acid copolymers in which a portion of the carboxylic acid groups in the copolymer are neutralized to salts containing metal ions. U.S. Pat. No. 3,264,272 discloses a composition comprising a random copolymer of copolymerized units of an alpha-olefin having from two to ten carbon atoms, an alpha, beta-ethylenically-unsaturated carboxylic acid having from three to eight carbon atoms in which 10 to 90 percent of the acid groups are neutralized with metal ions, and an optional third mono-ethylenically unsaturated comonomer such as methyl methacrylate or ethyl acrylate.
It is known that thermoplastic blends based on ionomers and polyamides have a combination of desirable properties (see U.S. Pat. Nos. 4,174,358, 5,866,658, 6,399,684, 6,756,443 and 7,144,938). For example, U.S. Pat. No. 5,866,658 discloses a blend of an ionomer dispersed in a continuous or co-continuous polyamide phase in the range of 60/40 weight % to 40/60 weight % used for molded parts exhibiting toughness, high gloss, abrasion/scratch resistance, and high temperature properties. U.S. Pat. No. 6,399,684 discloses similar blends also containing phosphorous salts such as a hypophosphite salt.
The ionomers include zinc ionomers or ionomers with mixtures of zinc and magnesium cations, which have a neutralization of 65 to 100 mole percent of the acid groups. A higher degree of neutralization, however, may cause high melt viscosity. To address the high melt viscosity of the blends of nylon and ionomer, one may use nylon of lower molecular weight and/or incorporate melt flow additives. For example, U.S. Pat. No. 6,756,443, “Ionomer/Polyamide Blends with Improved Flow and Impact Properties”, discloses an ionomer/polyamide blend with improved flow (e.g., lower melt viscosity) by incorporating a low molecular weight ethylene/acrylic acid copolymer (acid wax). The method adds complexity and also inevitably compromises properties, such as in abrasion and scratch resistance. U.S. Pat. No. 7,144,938 discloses similar blends also containing one or more esters of montanic acid.
U.S. Patent Application Publications 2005/0203253A1, 2005/020762A1, and 2006/0142489A1 disclose polyamides toughened with ionomers of ethylene copolymers containing a monocarboxylic acid and a dicarboxylic acid or derivative thereof. U.S. patent application Ser. No. 12/507,758 discloses a blend comprising a polyamide, an ionomer of an ethylene copolymer containing a monocarboxylic acid and a dicarboxylic acid or derivative thereof, and a sulfonamide. U.S. Patent Application Ser. No. 61/440,559 discloses a blend comprising a polyamide, an ionomer of an ethylene copolymer containing a monocarboxylic acid and a dicarboxylic acid or derivative thereof, and a second ionomer.
U.S. Pat. No. 6,680,082 describes mixed ion ionomers, particularly ionomers with a mixture of zinc and magnesium, calcium, sodium or lithium for metal coating powder applications. U.S. Patent Application Publication 2008/0097047 discloses blends of polyamides with mixed ion ionomers, including zinc and sodium mixtures.